P: Save option / cache optimisation Lightroom slideshows

Hi,

every time I want to play a Slideshow, it takes several minutes to calculate this, due to the fact, I have many big panoramas, HDRs etc.. It's been like this for years, app. it's not easy for Adobe to improve performance here. 

The real problem is though: the cache is deleted, as soon as it's played / you change to another program etc.; and if you wanna play it another time, it starts from scratch again - I keep wondering, why on earth has this been coded like that? Why can't it at least keep the cache of those images, instead of deleting this right away, or give an easy option to save this?
I can only export this as a video (or PDF) file, which again takes ages - and for this reason, the app is completely useless for showing slideshows to colleagues / clients etc., it simply always makes a bad impression, unless you export everything in advance (for which you don't always have the time).

Also when exporting, there's still no 4K option there, something like 20 years after this turned into a normal resolution for most users... Still max. HD, that's in my view hightly problematic, for core functionality like this.